The present invention relates generally to gas turbine engine lubrication systems and, more particularly, to systems for lubricating a fan drive gearbox in a geared gas turbine engine.
Gas turbine engines typically include, in axial flow series, a fan rotor, a low pressure compressor, a high pressure compressor, a combustor, a high pressure turbine, and a low pressure turbine. Air entering the low and high pressure compressors is compressed by alternating stages of rotor blades and vanes before entering the combustor. Within the combustor, fuel is injected, and the air is heated through combustion. The high and low pressure turbines expand the heated air to produce work before exhausting air from the gas turbine engine. The turbines produce work which is used to drive the low pressure and high pressure compressors as well as the fan rotor. In some gas turbine engines, a fan drive gearbox couples the fan rotor to the low pressure turbine, which drives the fan rotor. The gas turbine engine produces thrust from air exhausted from the low pressure turbine as well as from air that is driven by the fan and bypasses the engine core. The combination of thrust from bypass air and core air propels aircraft during flight.
During operation of the gas turbine engine, bearings within the fan drive gear box receive lubrication fluid from a main lubrication pump, which is typically driven by either the high pressure turbine or low pressure turbine through gearing. However, when the gas turbine engine is not operating, it may be possible for the fan to rotate without the aid of lubrication from the main lubrication pump. For example, wind blows through fan rotors of parked aircraft, causing rotation, sometimes referred to as windmilling. Windmilling fan rotors can reduce life of bearings within the fan drive gear box, particularly if such aircraft are parked for long periods of time. A need exists, therefore, for an auxiliary lubrication system to provide lubrication to fan drive gear box bearings during conditions when the main lubrication pump is not operating or is incapable of supplying lubrication fluid to the fan drive gearbox.